Does java8 forEach method use an iterator or not really? I google it to the bone, could not find it precisely. Only the fact that it will iterate in the same order the data are.
Any tips?
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1 Answer
The default implementation of Iterable#forEach is based on a iterator.
default void forEach(Consumer<? super T> action) {
Objects.requireNonNull(action);
for (T t : this) {
action.accept(t);
}
}
But in ArrayList is overridden to this, and not uses the iterator, it uses a for loop over its internal array
@Override
public void forEach(Consumer<? super E> action) {
Objects.requireNonNull(action);
final int expectedModCount = modCount;
@SuppressWarnings("unchecked")
final E[] elementData = (E[]) this.elementData;
final int size = this.size;
for (int i=0; modCount == expectedModCount && i < size; i++) {
action.accept(elementData[i]);
}
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
}
So it depends of its implementation.
Anyway, since this method is declared in Iterable interface, all iterables has this method.
2 Comments
bowmore
additionally : clients should not rely on any
Iterable implementation to use the underlying Iterator. Even when the current implementation does, future versions may not.
Holger
Since the caller does not know whether
forEach will use an Iterator or not, it is an “internal iteration” as that’s the whole point: the way, how the iteration is implemented, is hidden within the actual forEach implementation.